The present invention relates to an image reading apparatus which comprises an image reading unit for reading an image of a document, and a photographing unit for recording an image on a photosensitive member such as a film by exposure.
In general, an image reading apparatus (to be referred to as a xe2x80x9cdocument scannerxe2x80x9d hereinafter) for reading an image as digital image information using a photoelectric conversion element allows easy search, edit, and the like of read and stored information. However, the stored information is not legally endorsed. For example, the stored information cannot be used as an evidence in court. On the other hand, a microfilm on which an image is recorded by the microfilm photographing apparatus is legally endorsed. However, stored information does not allow easy search, edit, and the like.
In this way, the document scanner and microfilm photographing apparatus have opposite characteristics. Hence, an image reading apparatus which can utilize merits of both the microfilm photographing apparatus and document scanner by combining the photographing function of the microfilm photographing apparatus and the function of the document scanner may be proposed. That is, an image reading apparatus which allows easy search, edit, and the like of stored information, and can store information to be legally endorsed may be proposed.
A microfilm photographing apparatus (also called a rotary microfilm camera) for photographing an image on a document on a roll film by slit exposure while feeding the document at a constant speed is known. Also, an image reading apparatus for reading an image on a document by inputting it to a fixed photoelectric conversion element as a linear image while feeding the document is known. Note that the document includes not only a sheet but also thin media such as a card, label, and the like which bear images such as text, pictures, and the like.
FIG. 2 is a schematic view showing principal part of a conventional image reading apparatus.
Referring to FIG. 2, reference numeral 201 denotes a document serving as an object; 202, transparent guide glass windows provided on a convey path to photograph the conveyed document 201; 203A and 203B, lamps for illuminating the document to project an image onto a light-receiving element that performs photoelectric conversion or a microfilm; 204A and 204B, first mirrors which form an optical path for projecting the image of the illuminated document onto the light-receiving element and microfilm; and 205, a slit for splitting the optical path of the image illuminated with lamps into the light-receiving element side and the microfilm photographing side.
Reference numeral 206 denotes a second mirror for guiding the optical path split by the slit 205 toward the light-receiving element; 207, a third mirror for guiding the optical path split by the slit 205 toward the microfilm side; and 208 and 209, fourth and fifth mirrors for similarly guiding the optical path toward the microfilm.
Reference numeral 210 denotes a lens for projecting the image onto the light-receiving element; 211, a read sensor having a photoelectric conversion light-receiving element; 212, a microfilm lens for projecting the image onto the microfilm; 213, a microfilm; and 214, a light amount varying unit prepared by combining two polarization plates to adjust the amount of light to be projected onto the light-receiving element. In the light amount varying unit, the two polarization plates are arranged to overlap each other, and are pivoted so that their directions of polarization cross, thereby adjusting the transmission light amount.
The overall operation will be explained first. A document 201 is conveyed by a document convey unit (not shown) to the guide glass windows. When the conveyed document has reached an image photographing area inside the guide glass windows 202, it is illuminated by the lamps 203A and 203B. An image on the illuminated document is guided toward the photographing side via the first mirrors 204A and 204B, and its optical path is split into the read sensor side and microfilm photographing side by the slit 205 inserted between the first mirrors 204A and 204B, and the second and third mirrors 206 and 207.
Of the split optical paths, the image guided toward the read sensor side is projected onto and read by the read sensor by the lens 210 via the second mirror 206. The image read by the read sensor is captured as image data into a main body (not shown).
The other optical path split by the slit is guided to the third, fourth, and fifth mirrors 207, 208, and 209, and the microfilm 213 is exposed with the illuminated image via the microfilm lens 212.
Read by the read sensor and photographing on the microfilm are done using identical light source light, as can be seen from the arrangement of the optical path.
However, in the aforementioned prior art, since a document is illuminated using a single light source, wavelength ranges and light amounts respectively suitable for the light-receiving element that performs photoelectric conversion, and a photosensitive material such as a microfilm or the like cannot be selected. FIG. 6 shows an example of the characteristics of the photosensitive material and light-receiving elements depending on the light amount.
As can be seen from FIG. 6, when an exposure value is set to obtain an image having an appropriate density upon microfilm photographing, an appropriate image can be photographed on the microfilm. However, that exposure value results in an excessive light amount on the light-receiving element that performs photoelectric conversion, and the read image suffers fog and blurred text, resulting in poor reproduction of details.
Hence, the light amount varying unit such as a filter or the like described in the prior art is required on the optical path between the slit and light-receiving element so as to obtain an appropriate light amount on the light-receiving element. However, such unit may deteriorate image quality. Furthermore, as can be seen from FIG. 3, the light-receiving element that performs photoelectric conversion, and photosensitive material have different photosensitive characteristics.
As can be seen from the above description, when a single light source is used, it is very troublesome to adjust light source light to the photosensitive characteristics of both the light-receiving element and photosensitive material so as to obtain an optimal image, resulting in an expensive apparatus.
In order to allow density adjustment on the photoelectrically converted image side, the light amount varying unit described in the prior art is required, resulting in a complicated mechanism.
In addition, the density of the photographed image on the microfilm changes depending on the image density of the document upon photographing and the characteristics of a developing machine. In this case, the exposure value must be adjusted.
Likewise, density adjustment of the light-receiving element that performs photoelectric conversion is required in correspondence with an image on a document so as to read an image with higher quality.
Since the xe2x80x9cexposure valuexe2x80x94density output characteristicsxe2x80x9d of the light-receiving element and microfilm have no correlation, they must be individually set.
An image reading apparatus normally has a plurality of read resolutions, and changes the document convey speed in correspondence with the read resolution so as to take balance between the image quality and file size of the read image. Upon reading at high resolution, if the read speed per line is to be increased while setting a constant document speed, a high-speed, high-sensitivity photoelectric conversion element, and also a higher-speed image processing circuit are required, resulting in an expensive, complicated arrangement. Hence, the image reading apparatus changes and sets the document convey speed in correspondence with the read processing speed of a read processor while taking balance between the cost and arrangement. In this case, in the photographing apparatus using a photosensitive material such as a microfilm or the like, the amount of illumination light must be changed in correspondence with the convey speed for keeping the density of the photographed image constant, because the density of the image is defined by the amount of illumination light and an exposed time.
However, since the conventional apparatus illuminates a document using a single light source, setups that can satisfy the image qualities of both the photoelectric conversion side and film side cannot be obtained, because the changeable amount of the illumination light amount is limited.
In the conventional microfilm photographing apparatus, the feed speed of the document is always constant, and the photographing reduction factor can be switched within the range from ({fraction (1/24)}) to ({fraction (1/57)}). For this reason, the user prepares a plurality of photographing lenses having different reduction factors, and exchanges photographing lenses in accordance with the required reduction factor. The microfilm photographing apparatus changes the feed speed of the film in correspondence with the reduction factor, and takes a photo while the exposure value remains the same.
Also, the microfilm photographing device changes the brightness of illumination of a document since the developing condition of the photographed film, the density of the document, and the like may vary. For this purpose, the conventional microfilm photographing apparatus can adjust the brightness of a lamp that illuminates a document within the range from about 10% to about 50%. For example, the microfilm photographing apparatus adjusts the brightness of the lamp that illuminates a document by phase control of an AC power supply of a lamp such as a bulb, fluorescent lamp, or the like using a thyristor or the like, DC control for changing a voltage applied to a lamp, PWM control for controlling the amount of light of a lamp for turning on/off electric power applied to the lamp, and the like.
However, when the image reading apparatus mainly uses the function of the microfilm photographing apparatus to improve the read resolution, as a constant exposure value on a microfilm is set, the document convey speed can only be changed within the adjustment range of a lamp regulator that adjusts illumination of a document. For this reason, the image read resolution of the document scanner in which the read processing speed per line is fixed cannot be drastically changed.
When the read resolution is improved by mainly using the function of the document scanner so as not to disturb the performance of the document scanner, the following problem is posed.
The read resolution of the document scanner can be freely set by changing the document convey speed. For this reason, the document scanner normally has a read resolution range of about six times or more, i.e., a range from about 100 dots per inch (dpi) to about 600 dpi. Dots per inch indicate the number of dots per inch.
In this case, the convey speed of a film as the document changes about six times in correspondence with the read resolution. In the microfilm photographing apparatus that takes a photo by slit exposure, if the amount of light of a document illumination lamp is constant, the exposure value of a film increases in inverse proportion to the document convey speed, thus disturbing photographing at an appropriate density.
The document convey speed is added as new change condition, and conventional conditions such as the developing conditions, document density, and the like must also be taken into consideration. Hence, in order to maintain a constant density of the photographed image in consideration of all these conditions, the light amount of the document illumination lamp of the microfilm photographing apparatus must be varied within the range of around 12 times (around 100% to 8.4%).
For this reason, a lamp light amount control circuit for controlling the amount of light of illumination of a document must control the amount of light within the range of around 12 times or more. Since the light amount control range of a general circuit is around 10% to 50%, control that largely diverges from the general limit range of the amount of light is required, resulting in a very expensive circuit.
As a method of adjusting the amount of light by a relatively simple circuit arrangement, a plurality of illumination lamps may be prepared for the obverse and reverse sides of a document, and the amount of light may be controlled by controlling the number of ON illumination lamps. However, a plurality of illumination lamps, lamp control circuits, and the like are required, a size reduction of the apparatus cannot be attained, and the cost is high.
Therefore, upon simultaneously reading an image using the microfilm photographing apparatus and document scanner, one of an arrangement which sets a constant image read speed to fix the read resolution, and an arrangement which can change the image read speed, prepares for an expensive document illumination device, and adjusts the amount of light in correspondence with the document convey speed must be selected.
The present invention has been made to solve the conventional problems and has as its object to provide a highly reliable image reading apparatus in which both an image reading unit and photographing unit can obtain optimal images.
It is another object of the present invention to provide an image reading apparatus which can adjust the amount of light corresponding to the document convey speed by changing the degree of opening of a slit even when the document read speed is changed.
In order to solve the above problems and to achieve the above objects, an image reading apparatus according to the first aspect of the present invention is characterized by the following arrangement.
That is, an image reading apparatus which comprises an image reading unit which reads image information of a document, and a photographing unit which records an image of the document on a photosensitive material by exposure, comprises a first image illumination unit which illuminates the document read by the image reading unit, and a second image illumination unit which illuminates the document recorded by the photographing unit.
Also, an image reading apparatus according to the second aspect of the present invention is characterized by the following arrangement.
That is, an image reading apparatus comprises a document convey unit which conveys a document, an image reading unit which reads an image on the document conveyed by the document convey unit, a resolution selection unit which selects an image read resolution of the image reading unit, a photographing unit which has an exposure adjustment unit which adjusts an exposure value by controlling a degree of opening of a slit, and photographs an image on the document conveyed by the document convey unit, and a control unit which controls operations of the document convey unit and the exposure adjustment unit on the basis of the resolution selected by the resolution selection unit so as to adjust a convey speed of the document and the exposure value.